1) Field of the Invention
The present invention relates to a composite electronic component such as a resonator and a bandpass filter incorporating a plurality of circuit elements including an inductor thanks to its laminated structure and to a method of adjusting a resonant frequency and a center frequency in a passband of such a composite electronic component.
2) Description of the Prior Art
It is very difficult to obtain a desired frequency characteristic in an electronic component such as a resonator and a bandpass filter even if it is manufactured as designed. Therefore, in most cases, the frequency of the electronic component needs to be adjusted after being manufactured.
When the electronic component has a construction wherein independent circuit elements such as an inductor and a capacitor are soldered on a printed circuit board, its frequency can easily be adjusted by replacing the capacitor with another capacitor having a different capacity. However, in the case of a composite electronic component manufactured by laminating a plurality of electrodes, its frequency cannot be adjusted easily after being manufactured, in general. Therefore, it is necessary to construct the composite electronic component so that it allows its frequency to be adjusted easily.
The applicants of the present invention have proposed a frequency adjustment method of a resonator in Japanese Patent Application No. 1-289693. According to this method, a frequency adjusting capacitor electrode is formed on an outer surface of a resonator having a laminated structure and the frequency is adjusted by trimming the frequency adjusting capacitor electrode.
However, if the trimming is done using a laser beam or sand blast, an electrode formed of a malleable material such as Cu is extended, resulting in inaccurate trimming. Therefore, it is difficult to adjust the frequency desirably.
Especially, if the composite electronic component includes a high-frequency LC filter, more accurate trimming is necessary since slight change of the capacitor leads to great fluctuation of the frequency.